1. Field of the Invention
This invention relates to electro-static photo-copier machines which can operate to produce from positive document images pseudo-reversed one or alternatively from negative document images pseudo-reversed negative one.
2. Description of the Prior Arts
Generally speaking, in the case of the electro-static photo-copying technique, the process for providing positive copy images has been applied. Concerning positive document images (static latent images), a regular developing operation is applied by depositing the toner onto high potential regions on the drum surface, while, concerning negative document images (static latent images), a reverse developing operation is applied by depositing the toner onto low potential regions on the drum surface. It should be noted, however, static polarity and the like of the tone as adopted in the regular deposition mode is different from that adopted in the reverse deposition mode. As the result, in case of the image forming apparatus which is operable selectively one or the other depositing mode, these two differently operable depositing units are arranged in parallel in proximity of the drum surface so as to be capable of executing one selected-out mode only at one time by use of an operation change-over means. Or alternatively, either of the two different depositing units is exchanged in position with another, each time as occasion may desire, which procedure is naturally highly troublesome.
On the other hand, it may naturally be conceived to form negative copy images from positive document images by reliance or the reversing procedure. If a reverse deposition should be executed for this purpose, two different kinds of developing units must be adopted and arranged in order to perform the regular depositing operation as well as now reguisite positive-to-positive copying operation.
It may be further conceived to perform a copy image forming operation with use of negative document images as per se.
If, in this case, the regular depositing mode is employed for this purpose, two different kinds of developer must be employed and arranged again in this case serving for negative-to-positive developing and reverse developing operations.